The present invention relates to a printer head or printer of a so-called dye vaporization-thermal transfer type in which ink is vaporized or ablated to be transferred to a body to be recorded such as a printer paper sheet, and a method of manufacturing the recording apparatus.
In recent years, printers capable of outputting a full color image with a high quality have been increasingly required, particularly, for outputting a color image processed by a personal computer or an image recorded in a video camera or electronic still camera.
Examples of already-proposed color printers include a sublimation-thermal transfer type (or dye diffusion-thermal transfer type), fusion-thermal transfer type, ink jet type, electrophotography type, and thermally processed silver salt type. Among them, the dye diffusion-thermal transfer type and ink jet type are widely known as types capable of readily outputting a high quality image with a relatively simple apparatus.
The dye diffusion-thermal transfer type uses an ink ribbon or sheet coated with an ink layer formed by diffusing a transfer dye in a suitable binder resin at a high concentration. The ink ribbon or sheet is brought in close contact, at a specific pressure, with a so-called thermal transfer paper sheet coated with a dyeing resin capable of receiving the transferred dye. Then, the ink ribbon or sheet is given a thermal energy by a thermal head placed on the ink ribbon or sheet, with a result that the transfer dye is thermally transferred from the ink ribbon or sheet onto the thermal transfer paper sheet in accordance with the given thermal energy.
The above operation is repeated for each of the image signals associated with subtractive three primaries, yellow (Y), magenta (M), and cyan (C) separated from one color image, to thereby obtain a full color image having a continuous gradation.
FIG. 41 shows the configuration of a peripheral portion of a thermal head of a printer of this type.
A thermal head 70 is disposed opposite to a platen roller 71, between which an ink sheet 72 and a thermal transfer paper sheet 73 run by the rotating platen roller 71 in a state being pressed on the thermal head 70. The ink sheet 72 includes a base film 72b on which an ink layer 72a is provided, and the thermal transfer paper sheet 73 includes a paper sheet 73b whose surface is coated with a dyeing resin layer (dye receiving layer) 73a.
The ink in the ink layer 72a selectively heated by the thermal head 70 in accordance with an image to be printed is thermally diffused in the dyeing resin layer 73a of the thermal transfer paper sheet 73 heated in contact with the ink layer 72a. In this way, thermal transfer, for example, in a dot pattern is performed.
This dye diffusion-thermal transfer type is advantageous in miniaturizing the printer, making easy the maintenance of the printer, and enhancing the instancy of the printer, and further obtaining a high quality image comparable to that obtained by silver salt color photograph. The type, however, is disadvantageous in causing a large amount of waste products resulting from throwaway of the ink ribbon or sheet and in raising the running cost. Also since this type is required to use thermal transfer paper sheets, it presents a problem in further raising the cost.
The fusion-thermal transfer type enables transfer to normal paper sheets; however, since the type uses an ink ribbon or sheet, it is disadvantageous in causing a larger amount of waste products resulting from throwaway of the ink ribbon or sheet and in raising the running cost. Also the image quality obtained by this type is inferior to that obtained by silver salt photograph.
The thermally processed silver salt type is capable of obtaining a high image quality; however, since the type uses specialized photographic paper sheets and a throwaway type ribbon or sheet, it is disadvantageous in raising the running cost. Also this type has another problem in raising the apparatus cost.
The ink jet type is, as disclosed in Japanese Patent Publication Nos. Sho 61-59911 and Hei 5-217, classified into an electrostatic attraction type, continuous vibration generating type (piezo type), and a thermal type (bubble jet type). In this ink jet type, the printing is performed by jetting droplets of ink from a nozzle provided on a printer head to stick them to a printer paper sheet or the like.
The ink jet type, accordingly, is advantageous in lowering the running cost because it enables transfer to normal paper sheets and it does not use any ink ribbon or the like, and in substantially eliminating occurrence of waste products unlike the type using an ink ribbon or the like. The ink jet type, however, is disadvantageous in making it in principle difficult to obtain the density gradation in pixels, and hence to reproduce a high quality image comparable to that obtained by silver salt photograph for a short time unlike the above-described dye diffusion-thermal transfer type.
The electrophotographic type is advantageous in lowering the running cost and increasing the transfer speed; however, it is disadvantageous in making it difficult to obtain an image quality comparable to that obtained by silver salt photograph and in significantly raising the apparatus cost.
In summary, it becomes apparent that either of the above-described types fails to satisfy all requirements in terms of image quality, running cost, apparatus cost, transfer time, and the like.
Under such circumstances, as a color printer type capable of satisfying all the requirements, a so-called dye vaporization-thermal transfer type has been proposed, for example, in Japanese Patent Laid-open Nos. Hei 7-89107 and Hei 7-89108.
In this type, transfer operation is performed by heating ink on a transfer portion of a printer head to fly the ink by vaporization or ablation, and sticking the vaporized or ablated ink onto the surface of an object to be transferred such as a printer paper sheet disposed opposite to the transfer portion with a gap of about 50 to 100 .mu.m put therebetween.
The transfer portion includes an irregular ink holding structure in which a large number of pillars, each having the width or radius of about 2 .mu.m and the height of about 6 .mu.m, are erected with micro-intervals of about 2 .mu.m put therebetween. Also a heater is provided under the ink holding structure, to constitute a vaporizing portion.
The provision of such an ink holding structure exhibits the following effects:
(1) The ink is spontaneously supplied to the vaporizing portion by the capillary phenomenon; PA1 (2) The ink can be efficiently heated via a large surface area; PA1 (3) The ink in a specific amount can be usually held in the vaporizing portion by suitably setting the heights of the pillars; and PA1 (4) Since the surface tension of liquid generally has a negative temperature coefficient, the locally heated ink is applied with a force allowing the ink to flow to the outer peripheral portion kept at a low temperature; however, the movement of the ink toward the outer peripheral portion is suppressed at minimum by the ink holding structure, to thereby prevent lowering of the transfer sensitivity.
The provision of such an ink holding structure, accordingly, makes it possible to vaporize or ablate ink in an amount corresponding to the heating energy generated at the vaporizing portion and transfer the ink to a printer paper sheet or the like, and hence to attain continuous control of the transferred amount of the ink, that is, density gradation in pixels. As a result, the dye vaporization-thermal transfer type having the ink holding structure is capable of obtaining a high quality image comparable to that obtained by silver salt color photograph.
Since this type is not required to use any ink ribbon or the like, it is low in running cost, and since this type enables transfer to normal paper sheets by using ink having a high absorbing property for the normal paper sheets, it allows the reduction in the cost by use of normal paper sheets.
Since this type makes use of vaporization or ablation of ink (that is, a dye), it is not required not only to press the transfer portion of the printer head for heating the ink to an object to be transferred such as a printer paper sheet at a high pressure, but also to bring the transfer portion in contact with the object to be transferred. As a result, this type is advantageous in eliminating thermal fusion between an ink heating portion such as an ink ribbon and a printer paper sheet, which fusion has been often caused in other thermal transfer types.
As described above, in this recording head, dots are formed by fixing a dye on a body to be recorded, and accordingly, an interval between the two adjacent ones of the dye flying portions (heating or transfer portions) constitutes one dot interval. In other words, one dye flying portion is equivalent to one dot, and the dot intervals exert an effect on the resolution of a printed image. To be more specific, as the dot intervals become narrower, a higher resolution can be obtained.
From this viewpoint, one means for increasing the resolution is to make narrower each interval (dot interval) between the two adjacent ones of the dye flying portions; however, in the above-described recording head, a dye is supplied to one dye flying portion through one dye supply passage, and accordingly, if each interval between the two adjacent ones of the dye flying portions is made narrower for attaining an image with a high resolution; each interval between the two adjacent ones of the dye supply passages must be made narrower.
In other words, it is difficult to make narrower the above dot intervals unless the cross-sections of the dye supply passages are reduced. The reduction in cross-section of the dye supply passages, however, makes narrower the dye supply passages. This could lead to the possibility that the dye in an amount necessary and sufficient for transfer may not be supplied to the dye flying portions, and other problems that may make the method of manufacturing the head including the dye supply portions complicated and that its manufacturing yield reduced and its cost raised due to needs for the required enhancement of printer performance.
The present applicant has already proposed a recording apparatus capable of solving the above-described problems while making use of the advantages of the above-described dye flying structure in Japanese Patent Laid-open Nos. Hei 7-354113, 7-354114, and 7354115.
The common point, in the previously proposed recording apparatuses, for solving the above-described problems lies in that a recording head having dye flying portions for flying a dye to a body to be recorded is in contact with the body to be recorded in such a manner as to be tilted relative to the body to be recorded and in such a state, each dye flying portion is separated from the body to be recorded with a specific gap kept therebetween, and that branched passages branched from a common dye supply passage for supplying the dye are formed in order to simultaneously supply the dye from respective branched passages to a plurality of the dye flying portions.
FIG. 42 is a plan view showing an essential portion of the above-described recording head 20. In the recording head 20, a printed board 28 and a head chip 31 are bonded by means of a silicon based adhesive on an aluminum base 25 serving as a heat sink, and a cover 32 shown in FIG. 43 is mounted on the printed board 28 and the head chip 31 and bonded thereto by means of the same adhesive.
FIG. 44 is a sectional view of the above recording head 20. A portion, adapted to mount the printed board 28, of the base 25 is thinned by a thickness equivalent to that of the printed board 28, and the printed board 28 is mounted on the mounting portion of the base 25. In this mounting state, the total of the height of the printed board 28 and the height of a driver IC 26, for driving heaters, mounted on the printed board 28 is substantially equal to the height of the top surface of the head chip 31 mounted in parallel to the printed board 28.
The portion, on which the head chip 31 is adhesively bonded, of the base 25 has two grooves 33 for allowing the head chip 31 to be uniformly bonded on the base 25. To be more specific, an excess of the adhesive used for bonding the head chip 31 is escaped in the grooves 33. As shown in FIGS. 42 and 44, a connection portion between electrodes provided on the head chip 31 and the driver IC 26, and a connection portion between the driver IC and wiring provided on the printed board 28 are coated with a silicone resin based coating material JCR (junction coating resin) 27, which coating material is then thermally cured, in order to protect bonding wires for connection.
The printed board 28 has, as shown in FIGS. 42 and 44, a dye introducing hole 29 which passes through the base 25. A liquid dye 7 is introduced from the base 25 side between the cover 32 and the base 25 through the dye introducing hole 29. The cover 32 is adhesively bonded on the printed board 28 and the head chip 31 in such a manner as to sealingly cover a part of the printed board 28 and a part of the head chip 31. The inner surface portion of the cover 32 forms a common dye supply passage for receiving the dye 7 introduced through the dye introducing hole 29 and supplying the dye 7 into the above-described branched passages.
The recording head 20 is, as shown in FIG. 44, configured such that one end 25a, on the side on which the head chip 31 is provided, of the base 25 is brought in contact with a body 34 to be recorded while being tilted at a specific angle with respect to the body 34 to be recorded, so that as shown in FIG. 45, an interval between the center C.sub.1 of each dye flying portion 6 and the body 34 to be recorded can be kept constant.
In FIG. 44, the solid line arrow S designates the scanning direction of the recording head 20 upon printing, and the broken line arrow S' designates the return direction after printing. Accordingly, upon printing, the heaters are heated in accordance with a signal corresponding to image data supplied by way of a connector 30 provided at the leading end portion of the printed board 28, to vaporize the dye 7 from each dye flying portion 6, thereby flying the dye to the body 34 to be recorded. The wiring on the printed board 28 is connected to a FPC (flexible print circuit, not shown) through the connector 30. The apparatus is driven in accordance with a serial mode shown in FIG. 46 or a line mode shown in FIG. 47.
In the serial mode, as shown in FIG. 46, three pieces of dye storing portions 24, which store dyes of three primaries, Y (yellow), M (magenta) and C (cyan) (may be further added with black), are mounted three pieces of the recording heads 30 disposed in parallel to each other, respectively. These recording heads 20 are connected to respective movable pieces 23 engaged with a feed shaft 21 via respective connecting members 22. Since the feed shaft 21 is screw-engaged with the movable pieces 23, each recording head 20 is reciprocated in the direction shown by the arrow Y by turning of the feed shaft 21 driven by a drive source (not shown).
Meanwhile, the body 34 to be recorded, which is disposed opposite to the recording heads 20, is moved in the direction shown by the arrow X by feed rollers 18 for each line scanning of the recording heads 20. Accordingly, the body 34 to be recorded, which is positioned between a platen 19 and the recording heads 20, is printed by the recording heads 20.
In the line mode, as shown in FIG. 47, recording heads 20A, each having a length equivalent to the width of the body 34 to be recorded, are longitudinally disposed in the X-direction. These recording heads 20A are similarly mounted with dye storing baths 24A which store dyes of three primaries, Y (yellow), M (magenta), and C (cyan) (which may be further added with black).
The body 34 to be recorded, which is disposed opposite to the recording heads 20A and positioned between the recording heads 20A and the platen 19, is printed by the recording heads 20A, and after specific printing, the body 34 to be recorded is moved in the X-direction by rollers 18. In this way, the printing is subsequently performed.
FIG. 48 is a plan view showing part of the head chip 31 of the above-described recording head. The dye 7 introduced between the cover 32 and the base 25 as shown in FIG. 44 is supplied, by the capillary phenomenon, through a capillary region 36a in which the branched passages are formed by a base plate 1, partition walls 2 and a lid 3B, and is then supplied to the dye flying portions 6 by way of a between-partition wall region 36b and a communication region 36c.
As shown in FIG. 48, the partition walls 2 forming branched passages 8 project to the vicinity of intermediate portions between the lid 3B and the dye flying portions 6. The remaining half ranging from the intermediate portions to the dye flying portions 6, in which the partition walls 2 are not present, forms the communication region 36c. In the communication region 36c, the dye 7 passing through one branched passage 8 can be not only supplied linearly to the normal dye supply region to which the dye 7 should be mainly supplied by way of the branched passage 8 but also supplied curvedly to the two dye flying portions 6 on the adjacent branched passage sides as shown by the arrows.
FIG. 49 is a sectional view taken on line XXXXIX--XXXXIX of FIG. 48. In the capillary region 36a, since the dye 7 is stably supplied by the capillary phenomenon, there little occurs a fear of lacking of supply of the dye 7; however, in the between-partition wall region 36b and particularly in the communication region 36c, a meniscus 7a is formed as shown in FIG. 50. At the meniscus 7a, the thickness of the dye 7 becomes thin. The occurrence of the meniscus 7a causes an inconvenience that the supply of the dye 7 does not catch up with the flying of the dye 7 from each dye flying portion 6. Consequently, as shown in FIG. 51, a dye disappearance portion 37 occurs, which may cause interruption of the dye 7 in the course of the flow of the dye 7. It should be noted that in FIG. 51, the dye in the region equivalent to one dot is represented as points for an easy understanding.
If there occurs the interruption of the dye 7, such interruption is difficult to be recovered, which obstructs the supply of the dye 7 to the dye flying portions. As a result, the dye 7 in the dye flying portions 6 are gradually lost, making impossible the flying of the dye 7 in accordance with image information.
Also since the partition wall 2 is formed of a sheet-like organic matter by lithography, the shape of the partition wall 2 is not stabilized; the surface state of the partition wall 2 may be finely changed; and/or the distance between the edge 2a of the partition wall 2 and the dye flying portion 6 may be changed, with a result that the meniscus of the surface of the dye 7 may be changed, failing to obtain a specific height of the dye on the dye flying portion 6. That is to say, it becomes apparent that the above-described related art recording head has room for improvement.